Nicola Sturgeon made her clearest offer yet to help Ed Miliband into Downing Street at the BBC election debate.

Ed Miliband continues to rule out a formal coalition, sticking to his plan for a Labour majority - but the Labour leader has stopped short of ruling out a less formal deal with the SNP - or any other party for that matter.

So if no party gets an overall majority on May 7th, and they don't want to go into a formal coalition with other parties, what happens?

One way would be for two or more parties to go into a 'confidence and supply' arrangement - where the smaller parties would support a minority government on vital matters in return for some of their policies being enacted.

But how would that work?

What does the 'confidence' bit mean?

Smaller parties could be key to Ed Miliband making it to Downing Street (Image: Getty)

The smaller parties would agree to vote for (or possibly abstain on) the Queen's Speech set out by the minority government.

The Queen's Speech is thought of as the first test of a minority or coalition government. If any amendments to the Queen's Speech are passed by the House of Commons, or if the vote on the speech itself is lost, the Prime Minister must resign.

Tory Prime Minister Stanley Baldwin's 1924 King's Speech was defeated by 72 votes - he resigned the next morning and Ramsay MacDonald formed the first Labour government...which itself only lasted nine months.

The 'confidence' part also refers to supporting the government on votes of no-confidence in the government or its leadership.

What does the 'supply' bit mean?

The smaller parties would agree to support any bills necessary for the government to receive money to enact its policies.

Most importantly, this would mean voting for (or possibly abstaining on) any budget proposed by the minority government.

What's in it for the smaller parties?

(Image: Getty)

Although the arrangement rarely comes with guaranteed ministerial jobs, a confidence and supply deal would typically see some elements of the smaller party's manifesto enacted by the minority government in return for their support.

What's the downside?

(Image: Reuters)

Minority governments - even ones with a confidence and supply arrangement - tend to be weak and prone to a speedy collapse. There's not a lot in it for the junior party - and once the agreed parts of their manifesto have been tabled, there's little incentive for them to continue the arrangement.

However, people have been predicting the early collapse of the Coalition since the day it was formed and it's stuck together for five years.

We're in a whole new world of British politics and nobody's got a map.